I believe that Yamaha still uses Mercury lower units, and if that is still the case the pitot
opening is a very small hole (~1/8") in the front of the lower unit approximately 1 foot above the
skeg. If you cannot find it, buy a shop manual for your motor (a good idea anyway), or take it in
to a dealer to fix.

Once you've located the pitot opening, you'll need to clean it out with something. I've found that
a drill bit the proper size held between your fingers and twisted by hand works well. You will then
need to disconnect the pressure line from the back of your speedometer and blow the whole line out
with compressed air. The pressure line is usually clampped onto the barb on the back of the
speedometer with a plastic wire tie. You'll have to cut the wire tie with wire cutters, and then
put a new one on when you re-install the line.

There are also two connectors in the pressure line to the speedometer. One of them is in a
disconnect plug to your outboard motor. The other is inside the motor downhousing and connects to
the lower unit. If your lower unit has been removed for service recently, its possible that the
connector inside the downhousing was not reconnected properly, which would cause your speedo to stop
working also.

Personally, I'm betting on the pitot orifice being plugged with debris or aluminum oxide. I've had
to clean the one on my boat three times in the seven years that I've owned it (and its starting to
need it again). This is even though we operate on a relatively clean freshwater lake (Lake Travis).

Good luck with it,

Don W.



nfisherman wrote:
Help, my boat speedometer has quit working. I can keep track of my
speed with my GPS, but I'd like to get the speedometer to work. It is
operated by a pitot tube. I have checked behind the instrument panel
and everything appears to be fine. I believe that the pitot tube is
plugged somewhere, but I don't know where to look. I have followed
the tube to my outboard motor, a Yamaha F115, but I don't know which
opening is for the tube. Any suggestions short of taking the motor
apart?